DE1521440B2 - Process for stabilizing baths for electroless reductive metal deposition. Aren: Photocircuits Corp., Glen Cove, N.Y. (V.St.A.) - Google Patents

Description

1 2

The invention relates to a method for preferably in an amount of 0.002 to 0.15 mol / l,

Stabilizing baths for electroless deposition a complexing agent for copper (II) ions, for example

generation of metals on the catalytically active form of Rochelle salt, preferably in the 0.5 to 1.5 times

surfaces, namely on the deposition of iron, small amount of the moles of the copper salt, formaldehyde,

Nickel, cobalt, zinc, cadmium, tin, silver or 5, preferably in an amount of 0.4 to 3.5 mol / l,

Gold. Process for the electroless plating of an alkali metal hydroxide in an amount that

Metals for the formation of metal layers on suitable- preferably a pH value greater than 10.5 in the bath-

Neten surfaces are already known. Such liquid adjusts and a complexing agent for

Processes are used to distinguish between galvanic copper (I) ions, for example an inorganic one

see method using appropriate io cyanide, contains.

Baths referred to as working without current and cause the invention is based on the object of the

the continuous metal deposition on catalytic parts of the known process for the production of

effective surfaces. Copper coatings with consistently advantageous long

The autocatalytic bath solutions for the metal ger lifetime of the bath solution on the production deposition consist of an aqueous solution 15 of coatings to expand, made of iron, nickel, codes or the relevant metal salts, a Reduk- bait, zinc, cadmium, tin, silver or Gold exist, tion medium for the cations of the metal and The solution to this problem is that of a suitable complexing agent for this. The bath ion of the complexing agent used to produce the metal precipitate consists in adding a small amount of a cyanide compound, a water-soluble, stable complex, to the measuring liquid, which is dimensioned in such a way that it gives, which prevents that the metal cations inside are not sufficient to be able to reduce the autocatalytic separation of the solution from the reducing agent to metal formation process almost or completely to a standstill. The reduction process, and its concentration during the period of use, must be catalysis and is only essentially maintained for or in the next period of time.
Near a catalytically active surface instead. 25 As a result of this method according to the invention,

The aim of all processes for autocatalytic metals is the elements mentioned as well as mixtures of these

deposition is to find a bath composition, elements are extremely simple and effective

which limits the metal deposition to those areas can be fully deposited, whereby the

for which it is desired and the deposition in a different quality of the layer achieved by the deposition

avoids more districts. For this purpose, the concentration does not in any way have to be shifted from highly qualified

trations of the bath constituents according to deposits produced by analysis.

which is matched and, just like the pH value, which separates. The purity as well as the mechanical

Bath solution, monitored during operation. The pH properties of the deposition layer are opposite

Value depends essentially on the nature of the previously known process, noticeably improved,

Deposition bath and can have values between 35 Alkali cyanides have proven to be particularly suitable

for example 1 to 14 have. as well as nitriles; the concentration depends on

In all of the bath-to-bath structures known to date, the result was between 5 micrograms and 500 ml compositions of the kind that is of interest here, that grams per liter of bath liquid. As metal salts are it is not possible for the healthy metal present usually sulfates, chlorides, acetates or nitrates always to be kept in solution. The bath solutions show 4 ° used. The complexing agent for masking the rather, an inherent tendency to precipitate metal ions must be a water-soluble, stable grain metal particle. These metal precipitates represent a plex that provides a reduction of the metal cation Decomposition product of the bath and are already prevented in the solution, without the catalytic reallein therefore extremely undesirable because it hinders their production. For example, suitable grain presence causes the deposited metal 45 to be plexing agents, depending on the metal, ammonium as well films get rough, grainy and sometimes porous. organic complexing agents that contain one or more In addition, the fine metal particles act as cata- contain the following functional groups: primary Lytic germs or centers for the further metal amines (- NH2), secondary amines (= NH), deposition. However, this fact leads to a tiary amine (= N -), amino group (- NH) Carbosich further increasing decomposition of the bath and 50 xyl group (- COOH) and hydroxyl group (- OH). increased formation of metal sludge or, if the bath production must have undesirable Ne particles reaction on the walls of the bath can be avoided. So the reduction may be, for metallizing the same. In any case, the preparation containing the metal salt is used as a medium leads to this inherent tendency of the bath solution to be added only after the metal ions komdung of metal precipitates and are thus bound to a plex, otherwise an incipient Cutting limitation of the effective service life Reduction to the formation of metal nuclei leads to the host Usability of such baths. This grain. reduce the efficiency and stability of the bathroom, The process for auto- The concentrations of the various bath constituents catalytic Metal deposition significant. A distribution for baths according to the invention can be broad improvement of the stability and thus the effective 60 limits vary. As a general guide to the The service life of the known bath fluids is therefore composition can apply:

extremely desirable in order to obtain the initially water-soluble metal salt 0.002 to

to make these processes more economical. In q ^ q iyr _o j / i

this connection is already an aqueous bath- v ~ _m ~ i ~ u; iA ~~~ λ'τ u-

"..., .. Ai-ij TJ- ί · μ ·· ü .- Complexing agent 0.7 to

liquid for the deposition of copper coatings on 65 ^r lorn I d '

Surfaces of metals, plastics, ceramics and ZaM der

other insulating materials and other substances known-. w »j

become, in the case of a water-soluble copper salt, metal

Reducing agent 0.0002 to

2.5 mol / l

Cyanide compound 0.00001 to

0.06 mol / l

other common additives such as wetting agents.

Bath solutions according to the invention are particularly suitable for operation over long periods of time, provided that the used amounts of components of the bath solution are added again.

In the following, preferred exemplary embodiments of compositions are used according to the invention Bath liquids set up.

Example 1 * 5

A bath liquid was prepared according to the following formula:

Copper sulfate 0.05 mol / l

Diethylenetriamine tetraacetate 0.05 mol / l ^ao

Sodium Borohydride 0.009 Mol / L

Sodium cyanide ...... 0.008 mol / l

Lj pH 13

Temperature 25 ⁰ C

35

As a control, a bath of the same composition, but without cyanide, was prepared. This comparison bathroom decomposed after standing for 30 minutes; showed the bath according to the invention however, a useful life of more than 4 hours.

Example 2 The following bath was used for this:.,

OO

Copper sulfate 0.05 mol / l

N-hydroxyethylethylenediamine

triacetate 0.015 mol / l

Sodium cyanide 0.0016 mol / l

Sodium borohydride .... 0.008 mol / l

pH 13

Temperature 25 ° C

As a control, a bath of the same composition was again used, but used without cyanide.

The control bath stopped metal deposition after 30 minutes old; it fell apart then spontaneously. The cyanide bath, on the other hand, showed a useful life of more than 20 hours.

5o

Example 3

A bath according to the formula was used for this comparison:

Copper sulfate ......... 0.05 mol / l

N-hydroxyethylethylenediamine

triacetate -. · .. ..... 0.125 mol / l

Hydrazine sulfate 0.019 mol / l

Sodium cyanide. 0.001 mol / l

pH 9.8

. Temperature 43 ° C ^ö0

Again, a bath was used as a control, the formula of which only differs in that the cyanide is omitted. This control bath stopped the metal deposition after 30 micrograms / cm ^{2 of} copper had been deposited from it. The cyanide-containing bath, on the other hand, worked perfectly up to a deposited amount of copper of 0.1 mg / cm ² .

Example4
Formula of the bath:

Copper oxide 0.05 mol / l

Maleic acid 0.30 mol / l

Sodium cyanide 0.00001 mol / l

Sodium hypophosphite 0.5 mol / l

pH 4.5

Temperature 80 ° C

Here, too, a bath according to the above formula was used as a control, but without cyanide. aside from that a bath was prepared according to this formula, but with a cyanide content of 0.0001 mol / l. That Control bath without cyanide decomposed spontaneously with the formation of a reddish precipitate. That Bath with 0.0001 mol / l cyanide content did not deposit any metal and was therefore likewise unusable. The bathroom according to the formula above, with 0.00001 mol / l cyanide content, on the other hand, produced a glossy, dense one Copper film and worked flawlessly.

The amounts of the various bath constituents for the method according to the invention can be wide Limits vary. However, the following composition is typical for the preferred area:

Water soluble metal salt 0.002 to

0.60 mol / l

Complexing agent 0.7 to 10 times

the number of moles of the
Metal

Reducing agent 0.0002 to

2.5 mol / l

Cyanide compound 0.00001 to

0.06 mol / l

The amount of masking complexing agent depends essentially on the nature of the compound used away; a small excess, calculated on the metal content, is usually advantageous. For For best results, a wetting agent, such as, for example, should be added to the baths in a manner known per se an organic phosphate ester or oxyethyl sodium. It should be noted here that the Process according to the invention for improving the stability of autocatalytic baths, especially then has an extremely beneficial effect when such baths are operated over long periods of time and the consumed amounts of bath components, such as metal salt, reducing agent, etc., steadily or by To be replaced from time to time.

The method according to the invention is suitable for producing metal layers of practically any thickness on practically any surface and can be used, for example, for the production of Decorative and protective layers, markings and for the formation of conductive metal coatings on insulating materials.

Claims (4)

Patent claims: 1. Process for stabilizing baths for the electroless, reductive deposition of iron, Nickel, cobalt, zinc, cadmium, tin, silver or gold on surfaces that are catalytically active for this purpose, characterized in that the required for producing the metal deposit used bath liquid a small amount of a cyanide compound is added, which is measured in this way is that it is dense enough to close the autocatalytic deposition process or to bring them to a complete standstill and their concentration during the period of use essentially is maintained. 2. The method according to claim 1, characterized in that the bath solution is an inorganic one Cyanide or organic nitrile in a concentration between 5 micrograms / l and 500 milligrams / l is added. 3. The method according to claim 1 or 2, characterized in that a compound is used as the reducing agent the series of hydrogen boric compounds, hydrazines, hypophosphites, hydrosulfites, aminoboranes, Hydroxylamine and alpha-tri-oxymethylene is used. 4. The method according to any one of the preceding claims, characterized in that as a complexing agent in the bath solution used, a compound that contains at least one of the following functional groups: amino, imino, carboxyl and hydroxyl group is used.